The easiest way to kill George is of to keep him on the water so when you shoot him he doesn't go berserk and kill everyone.

But that said, I found some easier ways to kill him...

First make sure you turn on the power so you can get Juggernog.

Then get a really good gun, I recommend the Raygun, Matryoshka Dolls, or the Scavenger.

Ten make sure you get the Sickle and knife George when he's close to water (but out of it).

Then as soon as he gets mad, keep knifing him until he starts to run, then get him into the water and keep repeating.